With the score locked at 2-2 going into the final session, O'Sullivan came out from the interval all guns blazing, reeling off the last frames with breaks of 121, 69 and 124 - his fifth and sixth centuries of the competition.
O'Sullivan's victory means he breaks the record for most money won in a single season, with a potential half a million still on the cards ahead of the World Snooker Championship in April.
Held during Riyadh Season, the World Masters is the first-ever professional snooker tournament to take place in Saudi Arabia, offering a huge cash sum of £250,000 to the winner.
When quizzed on whether he would return to the Middle East, he said: “Hopefully. These are the tournaments you want to play in. Great tournament, great crowd, one table, music going during games. It was like going 25 years back when I was young.
“It all feels like a really nice festival. It's Riyadh season you know, you've got the boxing on Friday night, Formula 1 (this weekend)...everyone wants to get to Saudi.
“Saudi is like a powerhouse so if anyone can inject anything into snooker it’s the people who put this tournament on. Should be a 10-year contract tomorrow.”
Despite the loss, it has been a positive few days for Brecel, reaching a first final since September. He has been looking to recapture his best form ahead of his World Championship title defence in a few months.
O'Sullivan made a rapid start to the game, looking in far better form than he did in his semi-final against Judd Trump as he claimed the opening frame with a superb break of 95.
However, his Belgian opponent soon bounced back, continuing where he left off after his scintillating afternoon performance. The world champion pounced on a few sloppy shots from 'The Rocket', winning back-to-back frames with aggressive and ruthless potting.
Brecel looked on course to go 3-1 up, but O'Sullivan punished an error to rack up another big break of 94 to make it 2-2, before finishing off the contest in emphatic style. It is his 79th professional crown and fifth of the season, which includes major triumphs at the UK Championship and the Masters.
